Switch for radio-frequency currents



y 1949- R. G SHANKWEILER 2,475,464

' SWITCH FOR RADIO-FREQUENCY CURRENTS Filed April 8, 194

*g i i 57 INN/ HIE I INVENTOR. RHY 13.5HHNKWEILER Patented July 5, 1949SWITCH FOR RADIO-FREQUEN CY CURRENTS Ray G. Shankweiler, Cranbury, N.J., assignor to Radio Corporation of America, a corporation of DelawareApplication April 8, 1944, Serial No. 530,220

2 Claims.

This invention relates to improvements in switches and has for itsprincipal object to provide an improved switch for high frequency work,and one characterized by its freedom from coupling problems and by itsfreedom from undesired radiation beyond the switching points.

Another and important object of the invention is to provide an improvedand compact bank or assembly of sequence switches for radar and otherelectrical systems of the type wherein the several radio and audiofrequency channels are designed to be operated in a desired sequence andat a certain rate.

Another and specific object of the present invention is to provide animproved motor-driven switch assembly for synchronously switching (a) anaudio circuit, (b) a radio frequency circuit, a modulating circuit, andwherein the switching rate for the modulator circuit is at some fixedmultiple of the switching rate for the radio frequency and audiocircuits.

While the invention will be described as applied to a switch assemblyfor a frequency modulated radio locater system, such as the onedescribed in Patent No. 2,459,457, January 18, 1949, resulting fromcopending application Serial No. 527,292, filed March 20, 1944 in thename of Royden C. Sanders, Jr. and entitled Comparator circuits forradio locators, it is to be understood that the disclosure in thisrespect is merely illustrative and 1 should not be interpreted in alimiting sense.

Other objects and advantages together with certain preferred details ofconstruction will be apparent and the invention itself will be bestunderstood by reference to the following specification and to theaccompanying drawing, wherein:

Figure l is a sectional elevation of a switch panel including a switchassembly wherein the switch elements are designed, positioned andarranged in accordance with the present invention,

Figure 2 is a side elevational view partly in section showing the switchpanel of Fig. 1 supported upon a driving motor, and

Figure 3 is a sectional view taken on the line IIII1I of Fig. 2.

In the drawing I designates the casing of a motor or dynamotor having agear box 3 mounted on one end thereof as by means of a bracket 5 (Fig.3). The motor has a main shaft I which extends beyond the end of thecasing I and term-inates, within the gear box 3, in a reduction gearmechanism comprising a driving gear 9, a driven reduction gear I I, anda stub shaft I3 upon which the driven gear II is fixed. The frontsurface to of the gear box 3 comprises a switch panel and the stub shaftI3 extends to the front of the said panel at which point it is providedwith an eccentrically mounted ball bearing or cam I5 which serves, in amanner later described, to drive a pair of single-pole, double-throwswitches I1 and I9, respectively. A similar cam 2| (see Fig. 3) isaffixed to the opposite end of the main shaft '1 and provides areciprocating motion for opening and closing a single-pole, single-throwswitch 23. As shown in Fig. 3 the switch 23 is mounted upon aninsulating panel or disc 25 which is received within the casing I of themotor. This single-pole, single-throw switch 23 comprises a spring metalarm 21, which is secured to one end of the panel 25 as by means of astud 29. The switch arm 21 is provided at its free end with a contact3I. A cam follower 33, constituted of insulating material, is mountedintermediate the ends of the arm 21 and is biased (by the spring actionon the said arm) to bear against the peripheral surface of theeccentrically mounted cam 2|. The contact 3| on the free end of the arm21 is in register with a second contact which is carried by a U-shapedmember 3'! constituted of spring metal. The part 3'! is secured, on oneof its legs, to a rigid conductive arm 33% which is supported on a studon the panel or disc 25. The flexible arm of the U which carries thecontact 35 is biased outwardly into engagement with a flexible stop 4|Which may be bent, if desired, to fix the initial spacing between thecontacts 3| and 35 and thereby control the interval between the closingof said contacts.

The reed 21 of switch 23 (Fig. 3) is made so that its mass is high ascompared to the mass of the receiving contact 31. The spring tension ofthe reed 21 against the cam 2| is low, however, as compared to thespring tension of receiving contact 31 against the stop 4| In operation,the cam 2| is .in contact with the reed 33 and 21 only during the timethat the contacts are separated. When the contacts are closed, the reed27 is supported by receiving contact 37, since the spring tension of 31is many times that of the reed 2?. During operation, at the instant thecontacts make, the reed has energy stored in it due to its velocitytoward the receiving contacts. This energy is dissipated by momentarilylifting the receiving contact 31 oif the stop 35. After the energy isdissipated, the receiving contact returns to its position against stop35 since its spring tension is greater than the tension in reed 21.During this time, the cam 2! is not in contact with the reed 33 and 27.The break occurs when the cam again touches reed 21 and lifts it off thereceiving contact.

The circuit connections for the single-pole, single-throw switch 23 ofFig. 3 have been omitted from the drawing; however, since its arms 21,31 and its stop 4| are conductive it is apparent that all or less thanall of them may be utilized. When this switch is employed in thefrequency modulating sweep circuit of Sanders invention (Serial No.527,292) the cam 2i ordinarily operates to maintain the contacts 3i and35 closed during one-half of a complete cycle of revolution of the motorshaft 1'. In this case the main shaft 1 operates through the gearreduction mechanism 9, ll, l3 and cam l (at the opposite end of themotor casing) to maintain each pair of contacts on the single-poledouble-throw switches H and I9 closed for a smaller (but ad- .iustable)predetermined portion of each cycle.

As previously indicated, one of the problems which the present inventionsolves is that of obviating undesired radiation in a compact assembly ofsequence switches wherein one or more of the switches operate to makeand break a circuit carrying currents of radio frequency. in the usual(i. e. manually actuated) switch for selectively connecting one coaxialcable to another electrically similar cable, coupling problems may beminimized by so constructing the switch elements that they possesssubstantially the same characteristic impedance, per unit length, as thecables which they are designed to connect. In such a case the switchhousing forms a continuation of the outer (grounded) conductor of thecable and the shaft for actuating the switch is connected to the saidgrounded conductor through the bearings on which the shaft rotates sothat undesired radiations at the switching point are prevented frombeing broadcast. While the use of bearings and a grounded actuatingshaft are quite satisfactory in manually actuated switches, the frictionincident to the operation of such switches makes them undesirable in amotor driven sequence-switch assembly designed for continuous operation.The present invention may therefore be said to reside, in part, in theprovision of a switch wherein undesired radiations are confined to theswitch cavity, (and thereby prevented from affectin nearby circuits)without the use of a grounded shaft or equivalent friction-typeconnection.

As shown in Fig. 1, each .of the switches I1 and it comprises a metalarm or reed 43 having contacts 45 and 45a on its opposite faces and twostationary leads 4'! and 49 arranged along an axis normal to its reed45. An insulating extension 43a and a mechanical coupling 43 between thecam l5 and the said insulating extensions 43a serves to drive both reedsat a rate determined by the speed of the main shaft E (Fig. 2) and theratio of its gears 9 and H.

The receiving contact on each of the stationary leads 4?, 49 comprises abowed spring 51 and a p 5 p s 5| are restrained by their stops 53 in theposition shown in the drawing. Since the amplitude of the vibrating reed153 is fixed, the time during which the contacts make can be changed bymoving one or both of the receiving contacts away from or closer to thereed. Adjustment is accomplished by bending one or both of the stops 53.

Each of the single-pole double-throw switches ll and i9 is provided witha hollow T-shaped casing iii and 5t respectively. The vibrating reed lidof each switch is supported on an insulating insert i5! within the boreof the leg of the T and a similar insert 63 is provided in each crossarm of the T for supporting the leads 3'? and as for the receivingcontacts bl. It will be understood that when either switch (say switchit) is to serve a radio frequency transmission line the leads (ll, 49,and reed 43, 33a for that switch, its casing 59 and the cavity 59atherein, and the insulating inserts 6!, 63 should preferably be sodimensioned as to constitute an electrically matched continuation of theinner and outer conductors of the transmission line to which thebranches of the T are to be connected. (Thus, in the case of switch It,the dimensions of the said parts and the size of the cavity 59a was, inSanders case, so proportioned that the surge impedance through theswitch was of the order of ohms.) For the purpose of making suchconnections to the switch it each branch of its casing 59 is providedwith one or more threaded ports 65 for receiving a complementarilythreaded coupling bl (Fig. 2) for the outer conductor of thetransmission line. In the instant case each arm of the casing isprovided with two ports arranged at an angle of and the port which isnot in use is closed by a threaded cap 69.

The construction and operation of switches ll and i9, is quite differentfrom that of switch 23 of Fig. 3. In the case of switches l"; and themass of the vibrating reed 43, 42a is of no consequence since the reedis driven positively by means of the eccentrically mounted ball hearingand connecting member 48. The displacement of the reed is determinedentirely by the position of the eccentric. During its excursion fromside to side, the reed alternately contacts the receiving contacts 5|located on each side of the reed. As the reed moves to one side, itcomes into contact with the receiving contact 5| on that side, liftingit off its stop 53. Since the driving force applied to the reed ispractically unlimited as compared to the spring tension of El againstits stop 53, the spring 5! is lifted off the stop and flexed an amountequal to the travel of the reed. The spring tension of 5| must be highenough to overcome any tendency it may have to bounce when it is struckby the reed. Here, as in switch 23, it is desirable that the mass of thereceiving contact be as low as possible.

Reference has heretofore been made to the switch cavity 59a in which thecontacts 43, 45 and 5! operate and to the fact that undesired radiationat the switching points is confined to the cavity (and thereby preventedfrom affecting nearby circuits) without resorting to the use of agrounded shaft or equivalent friction type connection. This is achieved,in accordance with the invention by making the aperture 591) (throughwhich the insulating extension 43a vibration reed 43 extends to theexterior of the casing 59) small as compared to the wave length of thecurrent which the switch is designed to handle. When thus proportioned,this aperture 591) may be said to comprise an electrical filter and, inany event, has been found to reject or to attenuate the high frequencyfield originating within the cavity and which might otherwise beradiated beyond the switch casing. Thi flfi t rr 59?) operates in bothdirections, that is to say, it serves to prevent the ingress as well asthe egress of undesired radiations.

It will now be apparent that the present invention provides an improvedbank or assembly of sequence switches for high frequency work and onecharacterized by its compactness, by its freedom from couplin problemsand by its freedom from undesired radiations at or beyond the switchingpoints.

What is claimed is:

1. A switch assembly comprising a switch adapted to pass radio frequencycurrents of predetermined wave length and at least one other switchmounted adjacent to said radio frequency switch, said radio frequencyswitch comprising a casing having a cavity and an aperture whichcommunicates with said cavity, a plurality of switching elements withinsaid cavity and a lever arm for actuating said switching elementsextending from the interior of said cavity through said aperture out ofcontact with said casing to a point intermediate said switches, supplymeans for applying radio frequency currents of said predetermined wavelength to said switching elements, a lever arm for actuating said otherswitch terminatin adjacent to said point, common actuating means forsaid lever arms, said first mentioned lever arm being constituted ofinsulating material and the dimensions of the aperture in said casingthrough which said insulating lever arm passes being small as comparedto said wave length whereby the electric field about said switchingelements within said cavity is prevented from being transmitted throughsaid aperture to said adjacent switch.

2. A switch assembly comprising a motor having a housing and a rotatableshaft which extends through said housing, a switch within said housingand including an actuating element coupled in direct driven relationwith said rotatable shaft, a gear box mounted on said housing, aplurality of switches mounted in closely spaced relation on said gearbox, means for applying radio frequency currents of a predetermined Wavelength to at least one of said switches, said one of said switchescomprising a casing having a cavity containing the contact elements ofsaid switch and an aperture through which the actuating element for saidcontact extends, the dimensions of said aperture being small as comparedto said predetermined wave length and said actuating element comprisinga lever arm constituted of insulating material, whereby the electricfield within said cavity is prevented from being transmitted throughsaid aperture and affecting said other switches, and means connectingsaid radio frequency switch in sequential operating relation withrespect to said other switches through said gear box.

RAY G. SHANKWEILER.

REFERENQES CITED The following referenices are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 653,936 Murray July 17, 1900731,056 Jones June 16, 1903 1,541,497 Herz June 9, 1925' 2,180,948Basset Nov. 21, 1939 2,235,010 Chaffee Mar. 18, 1941 2,264,124 SchreinerNov. 25, 1941 2,312,723 Llewellyn Mar. 2, 1943 2,341,390 Scott Feb. 8,1944 2,408,779 Jenks et al Oct. 8, 1946 2,417,542 Carter Mar. 18, 1947

